"what are hypertrophy and hyperplasia? how would these processes affect the appearance of the thyroid under the microscope? how would the gross structure of the thyroid be affected"

Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells.

Hyperplasia is the enlargement of an organ or tissue caused by an increase in the reproduction rate of its cells.

In Hypertrophic Thyroid, thyroid follicles may be lined by cuboidal to columnar epithelium with central follicles tightly packed and smaller than normal.

Hyperplasias may contain individual trapped follicles. The generally accepted criteria for hyperplasia is a focal C-cell cluster less than five average follicular diameters or similarly small-sized clusters of C cells scattered in interfollicular spaces.

Hypertrophic thyroid is enlarged in size, appears to be swollen on inspection. Hyperplastic thyroid appears as a lump in the neck.

New species continue to evolve from existing species, creating the variety of life we see today.